The present invention relates to an autofocus apparatus, and in particular, to an autofocus apparatus which is used for a digital camera, a digital video camera and the like.
In an autofocus apparatus of a digital camera, a high frequency component of a video (image) signal from an image pickup device is used for an evaluation of focal control. The autofocus apparatus has the following excellent features; more specifically, there is substantially no existence of parallax, and in the case where a depth of field is shallow and a subject (object) is distant from a camera, it is possible to accurately focusing thereon. In addition, the autofocus apparatus requires no specific autofocus sensor, and has a very simple mechanism. Moreover, in the autofocus apparatus of a digital camera, in order to securely seize a shutter chance, there has been proposed a technique of shortening an AF run time.
For example, an autofocus camera disclosed in Japanese Patent Application Laid-Open No. 3-070273 detects a high-band component level of a video signal obtained from an image pickup device as a focus evaluation value every predetermined period, and thereby, performs an autofocus operation. Such an autofocus camera includes: search means; interpolation means; and focus evaluation value discrimination means. More specifically, the search means shifts (moves) a focus lens in a relatively coarse step from an infinity of subject distance to a closest focusing point, and thus, obtains a focus evaluation value for each step. The interpolation means makes an interpolation between a first maximum focus evaluation value obtained by the search means and a mutually adjacent focus evaluation value existing near to the first maximum focus evaluation value, and then, generates an interpolation focus evaluation value. The focus evaluation discriminating means discriminates a second maximum focus evaluation value from the interpolation focus evaluation value obtained by the interpolation means.
Moreover, an autofocus camera disclosed in Japanese Patent Application Laid-Open No. 3-068280 detects a high-band component level of a video signal obtained from an image pickup device as a focus evaluation value every predetermined period, and thereby, performs an autofocus operation. Such an autofocus camera includes: first search means; and second search means. More specifically, the first search means shifts (moves) a focus lens in a relatively coarse step from an infinity of subject distance to a closest focusing point, and thus, obtains a focus evaluation value for each step. The second search means shifts (moves) the focus lens to the vicinity of subject distance corresponding to a first maximum focus evaluation obtained by the first search means, and thereafter, shifts the focus lens in a fine step in the vicinity of the subject distance, and thus, obtains a second maximum focus evaluation value from a focus evaluation value for each fine step.
However, the aforesaid autofocus cameras disclosed in Japanese Patent Application Laid-Open No. 3-070273 and Japanese Patent Application Laid-Open No. 3-068280 have a problem that an AF running time becomes long depending upon the conditions. The following is a description on the cause of problem.
Usually, in AF of an electronic camera, first, a focus lens is shifted to infinity, and thereafter, an AF evaluation value is sampled while driving the focus lens to a near side, and thus, a peak of the AF evaluation value is obtained. In this case, when employing the methods disclosed in the aforesaid Japanese Patent Application Laid-Open No. 3-070273 and 3-068280 with respect to a subject near to the infinity, in order to obtain the peak 1 of the AF focus evaluation value of a relatively coarse step, the focus lens is driven to the near side from an in-focus position, and thereafter, the AF evaluation value in a fine step is sampled. Further, the focus lens is driven to the infinity side from the peak 1, and thereafter, a peak 2 of the AF evaluation value is obtained. For this reason, the focus lens is driven to the near side from the in-focus position so as to obtain the in-focus position, and thereafter, the focus lens is driven to the in-focus position.
Moreover, when employing the methods disclosed in the aforesaid Japanese Patent Application Laid-Open No. 3-070273 and 3-068280 with respect to a subject near to the infinity, the AF evaluation value is sampled from a focus infinity position; nevertheless, in two-time AF evaluation value sampling of relatively coarse step and fine step, as a focus lens operation, there are many return operations for the fine step AF evaluation value sampling. As seen from the above description, according to the technique disclosed in the aforesaid Japanese Patent Application Laid-Open No. 3-070273 and 3-068280, the AF running time is not always shortened.
Usually, in order to obtain a peak, at least three sampling AF evaluation values are required; for this reason, in the aforesaid two-time AF evaluation samplings, at least six sampling AF evaluation values are required. In the case where an in-focus position is obtained in six time or less AF evaluation value samplings, the AF running time can not be shortened even if there is no factor described above.
In general, a peak detection from three sampling AF evaluation values is not made because there is a noise, a pseudo peak or the like. Moreover, when the sampling number of AF evaluation values required for detecting a peak becomes much, there are many cases where the AF running time is not shortened.
It is an object of the present invention to provide an autofocus apparatus which shortens a time of driving a focus lens to an in-focus position so as to achieve a reduction of AF running time.
In order to solve the above problem, according to a first aspect, the present invention provides an autofocus apparatus comprising: an image pickup device for converting a subject light via a lens system into an electric signal, and for outputting the electric signal as an image data; A/D conversion means for A/D-converting the image data into a digital image signal; AF evaluation means for outputting an AF evaluation value on the basis of a high frequency component of a luminance signal of the digital image data; sampling means for sampling the AF evaluation value obtained by the AF evaluation means while shifting a focus lens position; and focus driving means for detecting an in-focus position on the basis of the AF evaluation value sampling result obtained by the sampling means, the autofocus apparatus further having: a first mode of shifting the focus lens at a fine step interval so as to sample an AF evaluation value, and for detecting an in-focus position on the basis of a sampling AF evaluation value; and a second mode of shifting the focus lens at a coarse step interval so as to sample an AF evaluation value, and detecting a rough in-focus position on the basis of the sampling AF evaluation value, and subsequently, shifting the focus lens at a fine step interval so as to sample an AF evaluation value in the vicinity of the rough in-focus position, and detecting an in-focus position on the basis of the sampling AF evaluation value, the autofocus apparatus being capable of selecting the first mode and the second mode.
Further, according to a second aspect, the present invention provides an autofocus apparatus comprising: an image pickup device for converting a subject light via a lens system into an electric signal, and for outputting the electric signal as an image data; A/D conversion means for A/D-converting the image data into a digital image signal; AF evaluation means for outputting an AF evaluation value on the basis of a high frequency component of a luminance signal of the digital image data; sampling means for sampling the AF evaluation value obtained by the AF evaluation means while shifting a focus lens position; focus driving means for detecting an in-focus position on the basis of the AF evaluation value sampling result obtained by the sampling means, and setting means for setting a plurality of focus lens shifting ranges for sampling the AF evaluation value, and for setting a sequence of detecting an in-focus position in each set shifting range, the autofocus apparatus detecting an in-focus position in each shifting range according to the sequence set by the setting means.
Further, according to a third aspect, the present invention provides an autofocus apparatus comprising: an image pickup device for converting a subject light via a lens system into an electric signal, and for outputting the electric signal as an image data; A/D conversion means for A/D-converting the image data into a digital image signal; AF evaluation means for outputting an AF evaluation value on the basis of a high frequency component of a luminance signal of the digital image data; sampling means for sampling the AF evaluation value obtained by the AF evaluation means while shifting a focus lens position; focus driving means for detecting an in-focus position on the basis of the AF evaluation value sampling result obtained by the sampling means, and setting means for setting a plurality of focus lens shifting ranges for sampling the AF evaluation value, and for setting a sequence of detecting an in-focus position in each set shifting range, the autofocus apparatus further having: a first mode of shifting the focus lens at a fine step interval so as to sample an AF evaluation value, and for detecting an in-focus position on the basis of a sampling AF evaluation value; and a second mode of shifting the focus lens at a coarse step interval so as to sample an AF evaluation value, and detecting a rough in-focus position on the basis of the sampling AF evaluation value, and subsequently, shifting the focus lens at a fine step interval so as to sample an AF evaluation value in the vicinity of the rough in-focus position, and detecting an in-focus position on the basis of the sampling AF evaluation value, the autofocus apparatus being capable of selecting the first mode and the second mode for each shifting range set by the setting means, and detecting an in-focus position in each shifting range according to the sequence set by the setting means.
Further, according to a fourth aspect, the present invention provides the autofocus apparatus wherein the autofocus apparatus automatically selects the first mode and the second mode.
Further, according to a fifth aspect, the present invention provides the autofocus apparatus wherein the autofocus apparatus automatically selects the first mode and the second mode in accordance with a focal length.
Further, according to a sixth aspect, the present invention provides the autofocus apparatus wherein the autofocus apparatus automatically selects the first mode and the second mode in accordance with a recording pixel aspect ratio.
Further, according to a seventh aspect, the present invention provides the autofocus apparatus wherein the autofocus apparatus automatically selects the first mode and the second mode in accordance with an F-number.
Other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.